Selective halogenation of 2,3-dihalopropenes



United States Patent 3,541,167 SELECTIVE HALOGENATION 0F 2,3-DIHALOPROPENES Reginald F. Roberts, Jr., Baton Rouge, La., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Mar. 22, 1968, Ser. No. 715,181 Int. Cl. C07c 21/02 US. Cl. 260-654 3 Claims ABSTRACT OF THE DISCLOSURE A process for the selective halogenation of 2,3-dihalopropenes of the formula wherein in each X is F, Cl, Br or I, said process producing only the 1,2,3-tri-halopropenes, which comprises reacting by contacting the above propenes with a tertiarybutyl hypohalite of the formula wherein Y is F, Cl, Br or I, in the presence or absence of a free-radical source.

BACKGROUND OF THE INVENTION The use of tertiary-butyl hypochlorite as a reagent for the free-radical chlorination of hydrocarbons is well established. The literature fails, however, to emphasize the extreme selectivity of this agent with 2,3-dihalopropenes. This ester is of such a high order of selectivity as compared to molecular halogens, that it in fact produces only one trihalogenated product.

SUMMARY OF THE INVENTION This invention is a novel process for the selective halogenation of 2,3-dihalopropenes, said process comprising reacting the propene with a tertiary-butyl hypohalite in the presence or absence of a free-radical source.

The use of tertiary-butyl hypohalites to selectively halogenate 2,3-dihalopropenes has the distinct advantage of producing only one trihalogenated derivative.

More particularly, this invention relates to a process for producing a single trihalogenated derivative of 2,3- dihalopropenes of the formula wherein each X is F, Cl, Br or I, said process comprising reacting by contacting the above propene with a tertiarybutyl hypohalite of the formula CHa\ CHa-C-O-Y wherein Y is F, Cl, Br or I.

The mole ratio of hypohalite/propene should gerierally be from about 1/ 100 to 1/ 1, and preferably from about 5/100 to /100. While reaction temperature is not critical, -80 to 40 C. is preferred. Pressure is also not critical, and atmospheric or the autogenous pressure is preferred.

It has been found that the yields of the instant process are not aflected by the presence or absence of a free- 3,541,167 Patented Nov. 17, 1970 SPECIFIC EMBODIMENTS Example No. 1.

Seven milliliters (ml.) of 2,3-dichlor0propene was pipetted into a lO-ml. nitrogen swept flask, equipped with a standard-taper ground-glass stopper. Under nitrogen flow, 1 ml. of tert-butyl hypochlorite was pipetted into and thoroughly mixed with the substrate. The flask was stoppered under nitrogen flow, and illuminated for a period of 50 minutes with a 100-watt electric-light bulb, situated at a distance approximately one inch from the top of the flask, and equipped with a shield of aluminum foil to contain approximately of the incident radiation. During this period of time, the temperature of the reaction mixture rose to approximately 35 C. from the heat radiated by the light bulb. A sample was withdrawn under nitrogen flow and analyzed by gas-phase chromatography. It was found to contain 88% 2,3-dichloropropene and 8.0% 1,2,3-trichloropropene, by weight.

The reaction mixture was then exposed to direct sunlight for a period of 34 minutes, at which time a second sample was found to contain 90% of the 2,3- and 8.4% of 1,2,3-trichloropropene (by Weight), indicating no further reaction. A S-ml. portion of this mixturewas next mixed (under nitrogen) with approximately 2 mls. of tert-butyl hypochlorite (second increment), and illuminated with a -watt bulb for about two hours. A sample of this final reaction mixture was found by anallysis to contain 16 .0% 1,2,3-trichloropropene.

I claim:

1. A process for the selective halogenation of 2,3- dihalopropenes of the formula wherein each X is F, Cl, Br or I, said process comprising reacting by contacting 1 to 100 moles of the above propene with 1 mole of a tertiary-butyl hypohalite of the formula wherein Y is F, Cl, Br or I to produce the corresponding 1,2,3-trihalopropene.

2. The process of claim 1 wherein the propene is 2,3- dichloropropene.

3. The process of claim 1 wherein the mole ratio of the tertiary-butyl hypohalite/propene is from 5/100 to 10/100.

References Cited UNITED STATES PATENTS 2,179,787 11/1939 Harford. 3,285,978 11/1966 Oga et al. 260-654 BERNARD H-ELFIN, Primary Examiner J. A. BOSKA, Assistant Examiner 

